Background Psychosocial problems refer to the difficulties faced by adolescents in different areas of personal and social functioning. Adolescents are vulnerable to psychosocial problems because of physical and physiological changes that occur in their body during this developmental stage. Therefore, this study was conducted to identify psychosocial problems among school going adolescents in Nepal. Methods A cross-sectional descriptive study was adopted. Nonprobability convenient sampling technique was used for selecting 287 adolescents. Ethical approval was taken from Nepal Health Research Council and self-administered structured questionnaire was used for data collection. Data collection was done in 2016. Descriptive statistics and chi-square test were used to analyze the data. Results The findings of this study show that 12.9 percent of adolescents had psychosocial problems. While categorizing psychosocial problems, the adolescents had internalizing problems (44.6%), attention deficit hyperactive disorder (ADHD) (25.8%), and externalizing problems (4.2%). There is association of age group and parent's marital status with psychosocial problems. Conclusion It is concluded that psychosocial problems (i.e., internalizing problems, ADHD, and externalizing problems) were prevalent among Nepalese school adolescents. Adolescents' age group and parent's marital status are associated with psychosocial problems. This study recommended that school authority, health professionals, and other professional related to child health and mental health should play an important role for the prevention and earlier recognition of and intervention for psychosocial problems.